The present invention relates to a pneumatic tire and, more particularly, to a pneumatic tire which is provided with a plurality of substantially quadrilateral land portions arranged on a tread and defined by two sets of main grooves of different angles with respect to a tire equatorial plane.
In the prior art, there is a pneumatic tire which is provided with a plurality of substantially quadrilateral land portions arranged on a tread and defined by two sets of main grooves of different angles with respect to a tire equatorial plane.
In this pneumatic tire, it is conceivable to form auxiliary grooves such as sipes in the land portions so as to improve the wet performance.
The auxiliary grooves such as the sipes are formed in the land portions, so that the edge factors are increased to improve the wet performance, but the rigidity of the land portions may be degraded and the deterioration of the dry performance may be caused.
In FIG. 13A, for example, a pair of main grooves 100 extending in the circumferential directions (i.e., in the directions as indicated by arrows A and B) and a pair of main grooves 102 intersecting the main grooves 100 define land portions 104 having generally parallelogram shapes. When the land portions 104 are halved in the tire circumferential directions by forming auxiliary grooves 106 in parallel with the main grooves 102, there arises a problem that the rigidity of the land portions 104 in the tire circumferential directions decreases.
On the other hand, when the auxiliary grooves 106 are formed in the generally parallelogram land portions 104 along the longer diagonal lines, as shown in FIG. 13B, there are formed two small land portions each of which has a substantially slender triangular shape. This formation raises a problem that the rigidity of the land portions 104 in the directions (i.e., in the directions of arrow C) perpendicular to the longitudinal direction of the auxiliary grooves 106 seriously decreases.
Considering the aforementioned facts, the invention has an object to provide a pneumatic tire which can improve the wet performance while keeping the rigidity of the land portions.
According to a first aspect of the invention, there is provided a pneumatic tire, in which a plurality of substantially quadrilateral land portions are arranged on a tread and defined by two sets of main grooves having different angles with respect to a tire equatorial plane and in which auxiliary grooves are arranged in said land portions, characterized: in that said land portions have diagonal lines of different lengths; and in that said auxiliary grooves are arranged at the central portions of said land portions and substantially along the shorter diagonal lines.
According to a second aspect of the invention, a pneumatic tire is characterized in that said auxiliary grooves are not opened in said main grooves.
According to a third aspect of the invention, a pneumatic tire is characterized in that said auxiliary groove have a length of no less than 30% but less than 70% of the length of said shorter diagonal lines.
According to a fourth aspect of the invention, a pneumatic tire is characterized in that the angle formed between said shorter diagonal lines and said auxiliary grooves is within xc2x120 degrees.
According to a fifth aspect of the invention, a pneumatic tire is characterized in that said auxiliary grooves are arranged substantially on said shorter diagonal lines.
According to a sixth aspect of the invention, a pneumatic tire is characterized in that said auxiliary grooves have a depth of no less than 30% of the depth of said main grooves.
According to a seventh aspect of the invention, a pneumatic tire is characterized in that end portion grooves opened in said main grooves are connected to the end portions of said auxiliary grooves.
According to an eighth aspect of the invention, a pneumatic tire is characterized in that said end portion grooves are opened in said main grooves which are the closet to the end portions auxiliary grooves.
According to a ninth aspect of the invention, a pneumatic tire is characterized in that the angle formed between said end portion grooves and said auxiliary grooves is obtuse.
According to tenth aspect of the invention, a pneumatic tire is characterized in that the angle formed between said end portion grooves and the neighborhood main grooves, in which said end portion grooves are not opened, is no more than 30 degrees.
According to an eleventh aspect of the invention, a pneumatic tire is characterized: in that said end portion grooves are formed on the two end portions of said auxiliary grooves; and in that one auxiliary groove is opened in one of the main grooves opposed to each other whereas the other auxiliary groove is opened in the other of the main opposed to each other.
According to a twelfth aspect of the invention, a pneumatic tire is characterized in that said end portion grooves are as deep as or shallower than said auxiliary grooves.
According to a thirteenth aspect of the invention, a pneumatic tire is characterized in that the depth of said end portion grooves is no less than 10% and no more than 30% of the depth of said main grooves.
According to a fourteenth aspect of the invention, a pneumatic tire is characterized in that the shortest distance between the end portions of said auxiliary grooves and said main grooves which are the closest to said end portions is no less than 15% of the length of said shorter diagonal lines.
According to a fifteenth aspect of the invention, there is provided a pneumatic tire, in which a plurality of substantially quadrilateral land portions are arranged on a tread and defined by two sets of main grooves having different angles with respect to a tire equatorial plane and in which auxiliary grooves are arranged in said land portions, characterized: in that said land portion has an auxiliary groove extending throughout from one side to another side; and in that said auxiliary groove includes: a central auxiliary groove portion inclined in the same direction as that of the shorter diagonal line of the land portion and arranged at the central portion of said land portion; end portion auxiliary groove portions extending in directions different from that of said central auxiliary groove portion and opened in the closest main grooves; and connection portions for smoothly joining said central auxiliary groove portion and said end portion auxiliary groove portions.
According to a sixteenth aspect of the invention, a pneumatic tire is characterized in that said connection portions are formed into arcuate shapes having a radius of curvature of no less than 3 mm and no more than 10 mm.
According to a seventeenth aspect of the invention, a pneumatic tire is characterized in that said central auxiliary groove portion has a length of less than 70% of the length of said shorter diagonal line.
According to an eighteenth aspect of the invention, a pneumatic tire is characterized in that the angle formed between said shorter diagonal line and said central auxiliary groove portion is within xc2x120 degrees.
According to a nineteenth aspect of the invention, a pneumatic tire is characterized in that said central auxiliary groove portion is arranged substantially on said shorter diagonal line.
According to a twentieth aspect of the invention, a pneumatic tire is characterized in that said central auxiliary groove portion has a depth of no less than 30% of the depth of said main grooves.
According to a twenty-first aspect of the invention, a pneumatic tire is characterized in that the angle formed between said end portion auxiliary groove portions and the neighborhood main grooves, in which said end portion auxiliary groove portions are not opened, is no more than 30 degrees.
According to a twenty-second aspect of the invention, a pneumatic tire is characterized in that said end portion auxiliary groove portions are as deep as or shallower than said central auxiliary groove portion.
According to a twenty-third aspect of the invention, a pneumatic tire is characterized in that the depth of said end portion auxiliary groove portions is no less than 10% and no more than 30% of the depth of said main grooves.
According to a twenty-fourth aspect of the invention, a pneumatic tire is characterized in that said auxiliary groove includes chamfered portions formed at the two corner portions of the opened portions of said auxiliary groove in the tread, when viewed in a section normal to the longitudinal direction at each point of the longitudinal direction.
According to a twenty-fifth aspect of the invention, a pneumatic tire is characterized in that said chamfered portions have a gently bulging sectional shape in said section normal to the longitudinal direction of said auxiliary groove.
According to a twenty-sixth aspect of the invention, a pneumatic tire is characterized in that the maximum of the depth H of said chamfered portions is no less than 5% and no more than 50% of the groove depth D of said auxiliary groove.
According to a twenty-seventh aspect of the invention, a pneumatic tire is characterized in that the maximum of the length L of said chamfered portions, as measured in parallel with the tread, in said section normal to the longitudinal direction of said auxiliary groove is no less than 5% and no more than 50% of the maximum width W, as taken in the tire axial direction, of the land portion having said auxiliary groove.
According to a twenty-eighth aspect of the invention, a pneumatic tire is characterized in that the depth H of said chamfered portions at each point in the longitudinal direction of said auxiliary groove is changed gently so that the change in the ground contact pressure which occurs inside the land portion under a lateral force may be small.
According to a twenty-ninth aspect of the invention, a pneumatic tire is characterized in that the depth H of said chamfered portions takes its maximum at the land portion ends of said auxiliary groove and at the central portion of the land portion.
Here will be described the effects of the pneumatic tire according to the first aspect of the invention.
The substantially quadrilateral land portions having the diagonal lines of the different lengths and defined by the two sets of main grooves of the different angles with respect to the tire equatorial plane can be exemplified by parallelogram land portions or the rhombic land portions.
By arranging the auxiliary grooves in the substantially quadrilateral land portions, the edge factors can be increased to improve the wet performance.
On the other hand, the auxiliary grooves are arranged substantially along the shorter diagonal lines of the land portions. Therefore, the parallelogram land portions or the rhombic land portions, for example, are divided into the two triangles approximating the equilateral triangles so that the decrease in the rigidity, as caused by providing the auxiliary grooves, of the land portions can be suppressed to the minimum.
Therefore, the pneumatic tire according to the first aspect of the invention can improve the wet performance while maintaining the excellent dry performance.
Therefore, the pneumatic tire as set forth in claim 1 can improve the wet performance while maintaining the excellent dry performance.
Here will be described the effects of the pneumatic tire according to the second aspect of the invention.
In the pneumatic tire according to the second aspect of the invention, the auxiliary grooves are not opened in the main grooves so that the decrease in the rigidity of the land portions can be suppressed as compared with the land portions having the auxiliary grooves opened in the main grooves, to maintain the high dry performance.
Here will be described the effects of the pneumatic tire according to the third aspect of the invention.
In the pneumatic tire according to the third aspect of the invention, when the auxiliary grooves not opened in the main grooves are formed in the land portions, the length of the auxiliary grooves is set to no less than 30% but less than 70% of the length of the shorter diagonal lines so that the decrease in the rigidity of the land portions can be suppressed while maintaining excellent water absorption, to make the wet performance and the dry performance compatible.
Here will be described the effects of the pneumatic tire according to the fourth aspect in the invention.
If the length of the auxiliary grooves exceeds 70% of the length of the shorter diagonal lines, on the other hand, the rigidity of the land portions deteriorates, to lower the dry performance.
Here will be described the effects of the pneumatic tire as set forth in claim 4.
The pneumatic tire according to the fourth aspect of the invention has an excellent effect that the decrease in the rigidity, as caused by providing the auxiliary grooves in the land portions, of the land portions can be suppressed to maintain the dry performance reliably.
If the angle formed between the shorter diagonal lines and the auxiliary grooves is beyond the range within xc2x120 degrees, the rigidity of the land portions decreases to lower the dry performance.
In order to suppress the decrease in the rigidity of the land portions, the angle formed between the shorter diagonal lines and the auxiliary grooves is preferably set in the range within xc2x110 degrees and is more preferably set in the range within xc2x15 degrees.
Here will be described the effects of the pneumatic tire according to a fifth aspect of the invention.
By arranging the auxiliary grooves substantially on the shorter diagonal lines, the land portions can be divided into the two triangles of substantially equal sizes so that the decrease in the rigidity of the land portions can be most effectively suppressed as compared with the case in which the auxiliary grooves are arranged at a given angle with respect to the shorter diagonal lines.
As a result, there is obtained an excellent effect that the dry performance can be maintained more reliably.
Here will be described the effects of the pneumatic tire according to the sixth aspect of the invention.
The depth of the auxiliary grooves is no less than 30% of the depth of the main grooves so that the water absorption can be maintained until the intermediate stage of wear.
Here will be described the effects of the pneumatic tire according to the seventh aspect of the invention.
When the auxiliary grooves (including the so-called xe2x80x9csipesxe2x80x9d) formed in the land portions are closed at two sides (that is, when the auxiliary grooves are not connected to any main groove), the water confined between the land portion ground contacting surfaces and the road surface instantly flows, as the land portions tread in the water pool of the wet road surface, from the ground contacting surfaces into the auxiliary grooves.
In the case in which the auxiliary grooves are closed on their two sides, when the auxiliary grooves are filled up with the water, the draining effect by the auxiliary grooves cannot be expected any more, because the water is no longer absorbed by the auxiliary grooves.
However, when the end portion grooves opened in the main grooves are connected to the end portions of the auxiliary grooves, the water sucked into the auxiliary grooves can be discharged through the end portion grooves into the main grooves so that the water between the ground contacting surfaces of the land portions and the road surface can be easily discharged, to improve the wet performance.
It is preferred from the standpoint of the better drainage into the main grooves that the end portion grooves are wider than the auxiliary grooves.
As a result, the pneumatic tire according to a seventh aspect of the invention has an excellent effect that the water between the ground contacting surfaces of the land portions and the road surface can be easily discharged to improve the wet performance as compared with the case of providing only the auxiliary grooves.
Here will be described the effects of the pneumatic tire according to the eighth aspect of the invention.
In the pneumatic tire according to the eighth aspect of the invention, the end portion grooves are opened in the main grooves which are the closest to the end portions of the auxiliary grooves, so that the length of the end portion grooves can be reduced, to discharge the water in the auxiliary grooves efficiently to the main grooves.
As a result, the pneumatic tire according to the eighth aspect of the invention has an excellent effect that it can further improve the wet performance.
Here will be described the effects of the pneumatic tire according to the ninth aspect of the invention.
In the pneumatic tire according to the ninth aspect of the invention, by forming an obtuse angle between the end portion grooves and the auxiliary grooves, the flow resistance can be suppressed to drain the water in the auxiliary grooves efficiently into the main grooves.
As a result, the pneumatic tire according to the ninth aspect of the invention has an excellent effect that it can further improve the wet performance.
Here will be described the effects of the pneumatic tire according to the tenth aspect of the invention.
In the pneumatic tire according to the tenth aspect of the invention, the angle formed between the end portion grooves and the neighborhood main grooves, in which the end portion grooves are not opened, is set within 30 degrees so that the decrease in the rigidity of the end portion grooves in the vicinity where the end portion grooves are opened to the main grooves can be suppressed, to suppress any peel, after the run, in the vicinity where the end portions are opened to the main grooves.
Here will be described the effects of the pneumatic tire according to the eleventh aspect of the invention.
In the pneumatic tire according to the eleventh aspect of the invention, one auxiliary groove is opened in one of the main grooves opposed to each other, and the other auxiliary groove is opened in the other of the main grooves opposed to each other. Therefore, the water sucked into the auxiliary groove can be efficiently discharged through the end portion grooves to both of the main grooves so that the water between the ground contacting surfaces of the land portions and the road surface can be more easily discharged to improve the wet performance better.
Here will be described the effects of the pneumatic tire according the twelfth aspect of the invention.
In the pneumatic tire according to the twelfth aspect of the invention, the end portion grooves are formed as deep as or shallower than the auxiliary grooves, thereby to suppress the local decrease in rigidity of the outer peripheral portions of the land portions. More preferably, by making the end portion grooves shallower than the auxiliary grooves, the rigidity of the outer peripheral edges of the land portions can be maintained as a whole, to achieve a rigidity which sufficiently resists the bending deformation of the land portions.
Here will be described the effects of the pneumatic tire according to the thirteenth aspect of the invention.
In the invention according to the thirteenth aspect of the invention, the depth of the end portion grooves is set to no less than 10% and no more than 30% of the depth of the main grooves so that the drainage at the initial stage of wear and the rigidity of the land portions are made compatible. If the depth of the end portion grooves is less than 10% of the depth of the main grooves, there cannot be obtained the drainage by the end portion grooves at the initial stage of wear. When the end portion grooves disappear due to wear, the tread surface is so roughened as to form irregularities therein, so that the sufficient draining effect is obtained by the recesses formed in the tread or the ground contacting face.
If the depth of the end portion grooves exceeds 30%, on the other hand, the rigidity of the land portions decreases so that the land portions are easily bent and deformed, to lower the dry performance.
Generally in the pneumatic tire according to the twelfth aspect of the invention, the end portion grooves have a depth of no less than 1 mm and no more than 4 mm.
As the depth of the end portion grooves is set to no less than 1 mm and no more than 4 mm, it is possible to make the drainage at the initial stage of wear compatible with the rigidity of the land portions.
Here, the sufficient draining action of the end portion grooves at the initial stage of wear cannot be obtained when the depth of the end portion grooves is less than 1 mm. When the end portion grooves disappear due to wear, the tread surface is so roughened as to form the irregularities therein, so that the sufficient draining effect is obtained by the recesses formed in the ground contacting surfaces of the land portions.
If the depth of the end portion grooves exceeds 4 mm, on the other hand, the rigidity of the land portions decreases and becomes susceptible to bending deformation, to deteriorate the dry performance.
Here will be described the effects of the pneumatic tire according to the fourteenth aspect of the invention.
When the auxiliary grooves are not opened in the main grooves, the rigidity of the land portions can be maintained by setting the shortest distance between the end portions of the auxiliary grooves and the main grooves which are the closest to the end portions to 15% or more of the length of the shorter diagonal lines.
If the shortest distance between the end portions of the auxiliary grooves and the main grooves the closest to the end portions is less than 15% of the length of the shorter diagonal lines, the end portions of the auxiliary grooves are so much close to the main grooves that the rigidity of the land portions decreases.
Here will be described the effects of the pneumatic tire according to the fifteenth aspect of the invention.
The substantially quadrilateral land portions, as defined by the two sets of main grooves of the different angles with respect to the tire equatorial plane, can be exemplified by the parallelogram land portions or the rhombic land portions.
Since the auxiliary grooves opened in the main grooves are arranged in the substantially quadrilateral land portions as described above, there is an increase in the edge factors for cutting the water film existing between the road surface and the ground contacting surfaces of the land portions. Moreover, the auxiliary grooves absorb the water existing between the road surface and the ground contacting surfaces of the land portions and drain the absorbed water to the main grooves, so that the wet performance is improved.
The end portion auxiliary groove portions, connected to the central auxiliary groove portion arranged at the centers of the land portions, are opened in the closest main grooves so that the water existing between the central portions of the land portions and the road surface is discharged by the shortest distance to the main grooves. Moreover, the central auxiliary groove portion and the end portion auxiliary groove portions are smoothly jointed by the connection portions, so that the water absorbed by the central auxiliary groove portion is smoothly discharged through the connection portions to the main grooves.
In addition, as the central auxiliary groove portion and the end portion auxiliary groove portions are smoothly jointed by the connection portions, the stress concentration at these linking portions between the central auxiliary groove portion and the end portion auxiliary groove portions can be suppressed to improve the crack-resistance properties.
Moreover, as the central auxiliary groove portion and the end portion auxiliary groove portions are smoothly jointed by the connection portions, the uneven distribution of the stress, as might otherwise be caused at the connection portions between the central auxiliary groove portion and the end portion auxiliary groove portions, can be suppressed, thereby preventing occurrence of the heel-and-toe wear.
In the pneumatic tire according to the fifteenth aspect of the invention, moreover, the center auxiliary groove portion is arranged at the central portion of the land portions with an inclination in the same direction as that of the shorter diagonal lines, so that the land portions are divided into the two triangles approximating the equilateral triangles thereby to prevent the land portions from becoming weak in a specific direction.
Therefore, the pneumatic tire as set forth in claim 15 has an excellent effect that it can improve the wet performance while maintaining the dry performance.
Here will be described the effects of the pneumatic tire according to the sixteenth aspect of the invention.
When the radius of curvature of the connection portions falls short of 3 mm, the stress concentration in the vicinity of the connection portions cannot be prevented, thereby increasing the possibility of forming the cracks. In addition, the stress becomes uneven in the vicinity of the connection portions to facilitate the heel-and-toe wear. At the connection portions, moreover, the flow resistance is increased to lower the drainage.
When the radius of curvature of the connection portions exceeds 10 mm, the center auxiliary groove portion is reduced so much that it cannot exhibit its unique effect (i.e., the effect to divide the land portions into the two triangles approximating the equilateral triangles so as to prevent the land portions from being weakened in a pacific direction).
Therefore, the connection portions preferably have the arcuate shape having the radius of curvature (as measured on the groove center line) of no less than 3 mm and no more than 10 mm.
As a result, the pneumatic tire according to the sixteenth aspect of the invention has excellent effects to suppress the occurrence of the cracks and the heel-and-toe wear, to prevent the land portions from being weakened in a specific direction, and to drain the absorbed water smoothly into the main grooves.
Here will be described the effects of the pneumatic tire according to the seventeenth aspect of the invention.
In the pneumatic tire according to the seventeenth aspect of the invention, the length of the center auxiliary groove portion is less than 70% of the length of the shorter diagonal lines so that the decrease in the rigidity of the land portions can be suppressed, to maintain the excellent dry performance.
Therefore, the pneumatic tire according to the seventeenth aspect of the invention has an excellent effect to make the dry performance compatible with and the wet performance.
Here will be described the effects of the pneumatic tire according to the eighteenth aspect of the invention.
When the angle formed between the shorter diagonal line and the center auxiliary groove portion is beyond the range within xc2x120 degrees, the rigidity of the land portions decreases, to deteriorate the dry performance.
In order to suppress the decrease in the rigidity of the land portions, the angle formed between the shorter diagonal lines and the center auxiliary groove portion is preferably set within xc2x110 degrees and more preferably within xc2x15 degrees.
Therefore, the pneumatic tire according to the eighteenth aspect of the invention has an excellent effect to maintain the dry performance reliably while suppressing the decrease in the rigidity of the land portions, which is caused by providing the auxiliary grooves in the land portions.
Here will be described the effects of the pneumatic tire according to the nineteenth aspect of the invention.
By arranging the center auxiliary groove potion substantially on the shorter diagonal lines, the land portions can be divided into the two triangles of substantially equal sizes so that the reduction of the rigidity of the land portions can be most efficiently suppressed, as compared with the case in which the center auxiliary groove portion is arranged at an angle with respect to the shorter diagonal lines.
Therefore, the pneumatic tire according to the nineteenth aspect of the invention has an excellent effect to maintain the dry performance more reliably.
Here will he described the effects of the pneumatic tire according the twentieth aspect of the invention.
The depth of the center auxiliary groove portion is no less than 30% of the depth of the main grooves so that the excellent drainage can be maintained.
Therefore, the pneumatic tire according to the twentieth aspect of the invention has an excellent effect to maintain the water absorption until the intermediate stage of wear.
Here will be described the effects of the pneumatic tire according to the twenty-first aspect of the invention.
In the pneumatic tire according to the twenty-first aspect of the invention, the angle formed between the end portion auxiliary groove portions and the neighborhood main grooves, in which the end portion auxiliary groove portions are not opened, is set within 30 degrees so that the decrease in the rigidity in the vicinity of the openings of the end portion auxiliary groove portions to the main grooves is suppressed, thereby to suppress the peel in the vicinity of the openings to the main grooves after the run.
Here will be described the effects of the pneumatic tire according to the twenty-second aspect of the invention.
In the pneumatic tire according to the twenty-second aspect of the invention, the end portion auxiliary groove portions are as deep as or shallower than the center auxiliary groove portion thereby to suppress the localized decrease in rigidity of the outer peripheral edge portions of the land portions. More preferably, by making the end portion auxiliary groove portions shallower than the auxiliary grooves, the rigidity of the outer peripheral edge portions of the land portions can be kept high as a whole to reliably resist bending deformation.
Here will be described the effects of the pneumatic tire according to the twenty-third aspect of the invention.
In the invention according to the twenty-third aspect of the invention, the depth of the end portion auxiliary groove portions is set to no less than 10% but less than 30% to make the drainage at the initial stage of wear compatible with and the rigidity of the land portions.
If the depth of the end portion auxiliary groove portions is less than 10% of the depth of the main grooves, it is impossible to obtain the sufficient draining action by the end portion auxiliary groove portions at the initial stage of wear.
If the depth of the end portion auxiliary groove portions exceeds 30% of the depth of the main grooves, on the other hand, the rigidity of the land portions decrease so much as to facilitate the bending deformation, thereby to deteriorate the dry performance.
In the pneumatic tire according to the twenty-second aspect of the invention, generally, the groove depth of the end portion auxiliary groove portions is no less than 1 mm and no more than 4 mm.
As the depth of the end portion auxiliary groove portions is set to no less than 1 mm and no more than 4 mm, the drainage at the initial stage of wear and the rigidity of the land portions are made compatible.
If the depth of the end portion auxiliary groove portions is less than 1 mm, it is impossible to obtain a sufficient draining action by the end portion auxiliary groove portions at the initial stage of wear.
If the depth of the end portion auxiliary groove portions exceeds 4 mm, on the other hand, the rigidity of the land portions decreases so much as to facilitate the bending deformation, thereby to deteriorate the dry performance.
Here will be described the effects of the pneumatic tire according to the twenty-fourth aspect of the invention.
The auxiliary groove includes chamfered portions formed, at the two corner portions of the opening portions of said auxiliary groove at the tread, overall the longitudinal length of the auxiliary groove at each point of the longitudinal direction, so that the contact pressure of the edge portions of the auxiliary grooves at the ground contacting time can be lowered. For the applications where the high lateral and longitudinal forces frequently applied, the effect to reduce the contact pressure as described above is exhibited quite significantly, to improve the resistance against partial wear, the wear performance and the running performance.
Here will be described the effects of the pneumatic tire according to the twenty-fifth aspect of the invention.
By forming the sectional shape of the chamfered portions into a gently bulging shape or a corner-rounded shape, it is possible to suppress the change in an abrupt ground contact pressure.
Here will be described the effects of the pneumatic tire according to the twenty-sixth aspect of the invention.
When the maximum of the depth H of the chamfered portions of the auxiliary grooves is less than 5% of the groove depth of the auxiliary grooves, there is a decrease in the effect to reduce the change in the contact pressure under the action of the lateral and longitudinal forces.
When the maximum of the depth H of the chamfered portions of the auxiliary grooves is larger than 50% of the groove depth D of the auxiliary grooves, the ground contact area is reduced too much.
Therefore, it is preferred that the maximum of the depth H of the chamfered portions is set to no less than 5% and no more than 50% of the groove depth D of the auxiliary grooves.
Therefore, the pneumatic tire according to the twenty-sixth aspect of the invention has an excellent effect that the contact pressure of the edge portions of the auxiliary grooves can be reduced to an optimum level.
Here will be described the effects of the pneumatic tire according to the twenty-seventh aspect of the invention.
When the maximum of the length L of the chamfered portions, as measured in parallel with the contact face, exceeds 50% of the maximum width W in the tire axial direction of the land portions having the auxiliary grooves, the ground contact area is reduced too much.
If the maximum of the length L of the chamfered portions, as measured in parallel with the contact face, is less than 5% of the maximum width W in the tire axial direction of the land portions having the auxiliary grooves, there is a decrease in the effect to reduce the change in the contact pressure under the action of the lateral and longitudinal forces.
Therefore, it is preferred that the maximum of the length L of the chamfered portions is set to no less than 5% and no more than 50% of the maximum width W of the land portions in the tire axial direction.
Therefore, the pneumatic tire according to the twenty-seventh aspect of the invention has an excellent effect to reduce the contact pressure of the edge portions of the auxiliary grooves to the optimum level.
Here will be described the effects of the pneumatic tire according to the twenty-eighth aspect of the invention.
The distribution of the contact pressure in the land portions under the lateral force varies according to the shape of the land portions and the routes of the auxiliary grooves, but by gently changing the depth of the chamfered portions of the auxiliary grooves at the individual points in the longitudinal direction, the distribution of the contact pressure can be made even to exhibit the effects to improve the resistance against partial wear, the wear performance and the running performance.
Here will be described the effects of the pneumatic tire according to the twenty-ninth aspect of the invention.
If the land portions do not have the chamfered portions at the land portion ends and the central portions of the auxiliary grooves, the contact pressure rises to an especially high level. By making the depth H of the chamfered portions larger than that of the remaining portions, there is an effect to homogenize the contact pressure.